U.S. patent application number 10/749902 was filed with the patent office on 2005-06-30 for quasi-parallel multichannel receivers for wideband orthogonal frequency division multiplexed communications and associated methods.
This patent application is currently assigned to Intel Corporation. Invention is credited to Belonozhkin, Alexander N., Maltsev, Alexander A., Sadri, Ali S., Sergeyev, Sergey E., Sergeyev, Vadim S..
Application Number | 20050141406 10/749902 |
Document ID | / |
Family ID | 34701120 |
Filed Date | 2005-06-30 |
United States Patent
Application |
20050141406 |
Kind Code |
A1 |
Maltsev, Alexander A. ; et
al. |
June 30, 2005 |
Quasi-parallel multichannel receivers for wideband orthogonal
frequency division multiplexed communications and associated
methods
Abstract
A quasi-parallel receiver may simultaneously receive signals
within several subchannels that comprise a wideband channel. The
receiver includes a subchannel filter selection switch that
provides a baseband signal to a selected one of a plurality of
subchannel low-pass filters. A heterodyne frequency generator
provides one of a plurality of heterodyne frequencies to convert an
RF signal received within a selected subchannel to the baseband
signal. The subchannel low-pass filters accumulate signal
information from an associated one of a plurality of subchannels
during a filter-input sampling interval. In some embodiments,
individual analog-to-digital converters receive the accumulated
signal outputs from an associated subchannel filter and generate
digital signals for a subsequent Fourier transformation. In some
embodiments, a normalized signal output may be provided to the
analog-to-digital converters, allowing the use of lower resolution
analog-to-digital converters. The analog-to-digital converters may
have sampling rates based on the subchannel bandwidth.
Inventors: |
Maltsev, Alexander A.;
(Nizhny Novgorod, RU) ; Sadri, Ali S.; (San Diego,
CA) ; Sergeyev, Sergey E.; (Nizhny Novgorod, RU)
; Belonozhkin, Alexander N.; (Nizhny Novgorod, RU)
; Sergeyev, Vadim S.; (Nizhny Novgorod, RU) |
Correspondence
Address: |
SCHWEGMAN, LUNDBERG, WOESSNER & KLUTH, P.A.
P.O. BOX 2938
MINNEAPOLIS
MN
55402-0938
US
|
Assignee: |
Intel Corporation
|
Family ID: |
34701120 |
Appl. No.: |
10/749902 |
Filed: |
December 29, 2003 |
Current U.S.
Class: |
370/203 ;
370/344 |
Current CPC
Class: |
H04B 1/0057 20130101;
H04L 27/2649 20130101; H04B 1/406 20130101; H04B 7/0413 20130101;
H04B 1/005 20130101; H04B 1/16 20130101; H04L 27/2608 20130101;
H04L 27/2653 20130101 |
Class at
Publication: |
370/203 ;
370/344 |
International
Class: |
H04J 011/00 |
Claims
What is claimed is:
1. A receiver comprising: a subchannel filter selection switch to
provide a baseband signal to a selected one of a plurality of
subchannel low-pass filters; and a heterodyne frequency generator
to provide one of a plurality of heterodyne frequencies to convert
a radio-frequency signal received within a selected subchannel to
the baseband signal, wherein the subchannel low-pass filters are to
accumulate signal information from an associated one of a plurality
of subchannels during a filter-input sampling interval.
2. The receiver of claim I further comprising a system controller
to generate a subchannel selection signal for the subchannel filter
selection switch and the heterodyne frequency generator, wherein
the selected one of the subchannel low-pass filters corresponds to
the selected subchannel of the plurality of subchannels, wherein
the heterodyne frequency generator is responsive to the subchannel
selection signal to generate one of the heterodyne frequencies to
convert radio-frequency signals within a corresponding one of the
subchannels within the filter-input sampling interval, wherein the
subchannel filter selection switch is responsive to the subchannel
selection signal to switch between the subchannel low-pass filters,
and wherein the filter-input sampling interval is to occur at least
as often as the inverse of a bandwidth of a subchannel.
3. The receiver of claim I wherein the receiver is a wideband
channel receiver further comprising radio-frequency circuitry to
receive orthogonal frequency division multiplexed signals in a
wideband channel comprising a plurality of subchannels, wherein
each subchannel low-pass filter corresponds to one of the plurality
of subchannels, wherein the subchannels have a subchannel
bandwidth, and wherein the subchannel low-pass filters have a
filter bandwidth of approximately half the subchannel
bandwidth.
4. The receiver of claim 1 wherein the receiver further comprises:
a whole-channel analog-to-digital converter; and a subchannel
filter output selection switch responsive to a subchannel filter
output selection signal to provide an accumulated signal output
from the selected subchannel low-pass filter to the whole-channel
analog-to-digital converter.
5. The receiver of claim 4 wherein a wideband channel comprises up
to four of the subchannels, the subchannels having bandwidths of
approximately 20-MHz, wherein the whole-channel analog-to-digital
converter comprises at least a 9-bit analog-to-digital converter
having a sampling rate of at least as great as a bandwidth of the
wideband channel, and wherein the heterodyne frequency generator is
to generate heterodyne frequencies during a filter-input sampling
interval for each subchannel, the filter-input sampling interval
being at least as great as the inverse of the bandwidth of the
subchannels, and wherein the subchannel filter output selection
switch responsive to the subchannel filter output selection signal
provides accumulated signal outputs from each of the subchannel
low-pass filters to the whole-channel analog-to-digital converter
once for each filter-output sampling interval, the filter-output
sampling interval being at least as great as the inverse of the
bandwidth of the subchannels.
6. The receiver of claim 1 further comprising a plurality of
subchannel analog-to-digital converters, the subchannel
analog-to-digital converters to receive an accumulated signal
output from a corresponding one of the subchannel low-pass
filters.
7. The receiver of claim 6 wherein the subchannels have bandwidths
of approximately 20-MHz, wherein the subchannel analog-to-digital
converters comprise at least 9-bit analog-to-digital converters
having sampling rates of at least as great as a bandwidth of the
subchannel, and wherein the heterodyne frequency generator is to
generate heterodyne frequencies or each subchannel during a
filter-input sampling interval, the sampling interval being at
least as great as the inverse of the bandwidth of the
subchannels.
8. The receiver of claim 6 further comprising an attenuator in a
radio-frequency signal path responsive to the subchannel selection
signal to attenuate the radio-frequency signal and provide a
normalized signal level for the selected subchannel filter and a
corresponding one of the subchannel analog-to-digital
converters.
9. The receiver of claim 1 wherein the heterodyne frequency
generator comprises: a fixed-frequency voltage-controlled
oscillator to generate a reference frequency; a digital synthesizer
to generate a selected one of a plurality of stepped frequencies in
response to a subchannel selection signal; and a frequency combiner
to combine the reference frequency and the selected one of the
stepped frequencies to generate one of the plurality of heterodyne
frequencies.
10. The receiver of claim 1 wherein the heterodyne frequency
generator comprises: a plurality of fixed-frequency
voltage-controlled oscillators, each fixed-frequency
voltage-controlled oscillator to generate a corresponding one of
the plurality of heterodyne frequencies; and a subchannel
heterodyne switch to select a heterodyne frequency from one of the
fixed-frequency voltage-controlled oscillators in response to a
subchannel selection signal.
11. The receiver of claim 1 further comprising: a plurality of
subchannel analog-to-digital converters, the subchannel
analog-to-digital converters to receive an accumulated signal
output from a corresponding one of the subchannel low-pass filters;
and a plurality of subchannel amplifiers to amplify the accumulated
signal outputs based on a gain control signal, the gain control
signal being generated for each subchannel.
12. The receiver of claim 1 wherein the receiver further comprises
radio-frequency circuitry to receive signals over a single
subchannel comprising a plurality of spatial channels, wherein the
radio-frequency circuitry comprises an antenna selection switch to
select one of a plurality of antennas corresponding to one of the
spatial channels, wherein each subchannel low-pass filter
corresponds to one of the spatial channels, wherein the heterodyne
frequency generator is to provide a single heterodyne frequency to
convert radio-frequency signals of the single subchannel to
baseband signals, and wherein the subchannel low-pass filters are
to accumulate signal information for a corresponding one of the
spatial channels.
13. The receiver of claim 12 further comprising: a plurality of
spatial channel analog-to-digital converters, the spatial channel
analog-to-digital converters to receive an accumulated signal
output from a corresponding one of the subchannel low-pass filters;
and a digital signal processor to perform fast Fourier transforms
on bit streams from the spatial channel analog-to-digital
converters and to generate a parallel group of time-domain samples
for each of a plurality of symbol-modulated subcarriers that
comprise the single subchannel.
14. The receiver of claim 3 wherein the subchannels comprise a
plurality of symbol-modulated orthogonal subcarriers, and wherein
each orthogonal subcarrier of a corresponding subchannel has a null
at substantially a center frequency of other subcarriers of the
corresponding subchannel.
15. The receiver of claim 14 wherein prior to reception by the
receiver, the subcarriers are to be individually modulated in
accordance with an individual subcarrier modulation assignment
comprising one of no modulation, binary phase shift keying (BPSK),
quadrature phase shift keying (QPSK), 8 PSK, 16-quadrature
amplitude modulation (16-QAM), 32-QAM, 64-QAM, 128-QAM, and
256-QAM.
16. A method comprising: accumulating signal information from a
selected one of a plurality of subchannels during a filter-input
sampling interval in an associated subchannel low-pass filter;
repeating the accumulating for others of the subchannels during the
filter-input sampling interval; and performing a fast Fourier
transform on digital signals generated from the accumulated signal
information from the plurality of subchannels to generate a
received orthogonal frequency division multiplexed symbol.
17. The method of claim 16 further comprising: providing a baseband
signal to a selected one of a plurality of subchannel low-pass
filters during the filter-input sampling interval; providing,
during the filter-input sampling interval, one of a plurality of
heterodyne frequencies to convert a radio-frequency signal received
within the selected subchannel to the baseband signal.
18. The method of claim 17 further comprising: generating a
subchannel selection signal to responsively provide one of the
heterodyne frequencies to downconvert radio-frequency signals
within a corresponding one of the subchannels within the
filter-input sampling interval; and switching between the
subchannel low-pass filters in response to the subchannel selection
signal.
19. The method of claim 18 wherein the subchannel selection signal
is generated to provide the filter-input sampling interval at least
as often as the inverse of a bandwidth of a subchannel.
20. The method of claim 18 further comprising: receiving an
accumulated signal output from a corresponding one of the
subchannel low-pass filters; and performing an analog-to-digital
conversion on the accumulated signal output.
21. The method of claim 20 further comprising: attenuating, in
response to the subchannel selection signal, the radio-frequency
signals to provide a normalized signal level for the selected
subchannel filter and to perform an analog-to-digital conversion on
the accumulated signal output.
22. The method of claim 17 further comprising: generating a
constant reference frequency; generating, with a digital
synthesizer, a selected one of a plurality of stepped frequencies
in response to a subchannel selection signal; and combining the
reference frequency and the selected one of the stepped frequencies
to generate one of the plurality of heterodyne frequencies.
23. The method of claim 17 further comprising: performing
individual analog-to-digital conversions on accumulated signal
outputs from corresponding ones of the subchannel low-pass filters;
and individually amplifying the accumulated signal outputs based on
a gain control signal for each subchannel.
24. The method of claim 17 further comprising: receiving, with a
plurality of spatially diverse antennas, an orthogonal frequency
division multiplexed symbol over a single subchannel comprising a
plurality of spatial channels; and generating an antenna selection
signal to select one of the antennas corresponding to one of the
spatial channels, wherein each subchannel low-pass filter
corresponds to one of the spatial channels, wherein the heterodyne
frequency generator provides a single heterodyne frequency to
convert radio-frequency signals of the single subchannel to
baseband signals, and wherein the subchannel low-pass filters
accumulate signals for a corresponding one of the spatial
channels.
25. A system comprising: a substantially omnidirectional antenna; a
subchannel filter selection switch to provide a baseband signal to
a selected one of a plurality of subchannel low-pass filters; and a
heterodyne frequency generator to provide one of a plurality of
heterodyne frequencies to convert a radio-frequency signal received
within a selected subchannel to the baseband signal, wherein the
subchannel low-pass filters are to accumulate signal information
from an associated one of a plurality of subchannels during a
filter-input sampling interval.
26. The system of claim 25 further comprising a system controller
to generate a subchannel selection signal for the subchannel
selection switch and the heterodyne frequency generator, wherein
the selected one of the subchannel low-pass filters corresponds to
the selected subchannel of the plurality of subchannels, wherein
the heterodyne frequency generator is responsive to the subchannel
selection signal to generate one of the heterodyne frequencies to
convert RF signals within a corresponding one of the subchannels
within the filter-input sampling interval, wherein the subchannel
selection switch is responsive to the subchannel selection signal
to switch between the subchannel low-pass filters, and wherein the
filter-input sampling interval is to occur at least as often as the
inverse of a bandwidth of a subchannel.
27. The system of claim 26 further comprising: a plurality of
subchannel analog-to-digital converters, the subchannel
analog-to-digital converters to receive an accumulated signal
output from a corresponding one of the subchannel low-pass filters;
and an attenuator in a radio-frequency signal path responsive to
the subchannel selection signal to attenuate the radio-frequency
signal and provide a normalized signal level for the selected
subchannel filter and a corresponding one of the subchannel
analog-to-digital converters.
28. A machine-readable medium that provides instructions, which
when executed by one or more processors, cause said processors to
perform operations comprising: accumulating signal information from
one of a plurality of subchannels during a filter-input sampling
interval in an associated subchannel low-pass filter; repeating the
accumulating for others of the subchannels during the filter-input
sampling interval; and performing a fast Fourier transform on
digital signals generated from the accumulated signal information
from the plurality of subchannels to generate a received orthogonal
frequency division multiplexed symbol.
29. The machine-readable medium of claim 28 wherein the
instructions, when further executed by one or more of said
processors, cause said processors to perform operations further
comprising: providing a baseband signal to a selected one of a
plurality of subchannel low-pass filters during the filter-input
sampling interval; providing, during the filter-input sampling
interval, one of a plurality of heterodyne frequencies to convert a
radio-frequency signal received within the selected subchannel to
the baseband signal.
30. The machine-readable medium of claim 28 wherein the
instructions, when further executed by one or more of said
processors, cause said processors to perform operations further
comprising: generating a subchannel selection signal to
responsively provide one of the heterodyne frequencies to
downconvert radio-frequency signals within a corresponding one of
the subchannels within the filter-input sampling interval; and
switching between the subchannel low-pass filters in response to
the subchannel selection signal.
Description
TECHNICAL FIELD
[0001] Embodiments of the present invention pertain to wireless
electronic communications, and in some embodiments, the present
invention pertains to orthogonal frequency division multiplexed
communications.
BACKGROUND
[0002] Orthogonal frequency-division multiplexing (OFDM) is an
example of a multi-carrier transmission technique that uses
symbol-modulated orthogonal subcarriers to transmit information
within an available spectrum. Many modern digital communication
systems, including wireless local-area networks (WLANs), are using
symbol-modulated orthogonal subcarriers as a modulation scheme to
help signals survive in environments having multipath reflections
and/or strong interference. One problem with many conventional
systems that use symbol-modulated subcarriers is that channel
bandwidth is limited to the bandwidth of the individual channels.
Some conventional wireless communication systems, such as WLANs
that implement OFDM communications, communicate using channels that
may only have about a 20-MHz bandwidth. Thus, there are general
needs for systems and methods for receiving wider bandwidth
communications.
BRIEF DESCRIPTION OF THE DRAWINGS
[0003] The appended claims are directed to some of the various
embodiments of the present invention. However, the detailed
description presents a more complete understanding of embodiments
of the present invention when considered in connection with the
figures, wherein like reference numbers refer to similar items
throughout the figures and:
[0004] FIG. 1 is a block diagram of a receiver in accordance with
some embodiments of the present invention;
[0005] FIGS. 2A and 2B illustrate subchannel analog-to-digital
converter circuitry in accordance with some embodiments of the
present invention;
[0006] FIG. 3 illustrates a heterodyne frequency generator in
accordance with some embodiments of the present invention;
[0007] FIGS. 4A and 4B illustrate subchannel analog-to-digital
converter circuitry with corresponding amplifiers in accordance
with some embodiments of the present invention;
[0008] FIG. 5 illustrates radio-frequency (RF) and front-end
circuitry in accordance with some embodiments of the present
invention;
[0009] FIGS. 6A, 6B and 6C illustrate timing diagrams in accordance
with some embodiments of the present invention; and
[0010] FIG. 7 is a flow chart of a signal reception procedure in
accordance with some embodiments of the present invention.
DETAILED DESCRIPTION
[0011] The following description and the drawings illustrate
specific embodiments of the invention sufficiently to enable those
skilled in the art to practice them. Other embodiments may
incorporate structural, logical, electrical, process, and other
changes. Examples merely typify possible variations. Individual
components and functions are optional unless explicitly required,
and the sequence of operations may vary. Portions and features of
some embodiments may be included in or substituted for those of
others. The scope of embodiments of the invention encompasses the
full ambit of the claims and all available equivalents of those
claims. Such embodiments of the invention may be referred to,
individually or collectively, herein by the term "invention" merely
for convenience and without intending to voluntarily limit the
scope of this application to any single invention or inventive
concept if more than one is in fact disclosed.
[0012] FIG. 1 is a block diagram of a receiver in accordance with
some embodiments of the present invention. Receiver 100 may be part
of a wireless communication device and may receive orthogonal
frequency division multiplexed (OFDM) communication signals. In
some embodiments, receiver 100 may receive an OFDM symbol on a
wideband communication channel. The wideband channel may comprise
one or more subchannels. The subchannels may be frequency-division
multiplexed (i.e., separated in frequency) and may be within a
predetermined frequency spectrum. The subchannels may comprise a
plurality of orthogonal subcarriers. In some embodiments, the
orthogonal subcarriers of a subchannel may be closely spaced OFDM
subcarriers. To achieve orthogonality between the closely spaced
subcarriers, the subcarriers of a particular subchannel may have a
null at substantially a center frequency of the other subcarriers
of that subchannel.
[0013] In accordance with some embodiments, the subcarriers may
have been symbol-modulated in accordance with individual subcarrier
modulation assignments. This may be referred to as adaptive bit
loading (ABL). Accordingly, one or more bits may be represented by
a symbol modulated on a subcarrier. The modulation assignments for
an individual subchannel may be based on the channel
characteristics or channel conditions for that subcarrier, although
the scope of the invention is not limited in this respect. In some
embodiments, the subcarrier modulation assignments may range from
zero bits per symbol to up to ten or more bits per symbol. In terms
of modulation levels, the subcarrier modulation assignments may
comprise, for example, binary phase shift keying (BPSK), which
communicates one bit per symbol, quadrature phase shift keying
(QPSK), which communicates two bits per symbol, 8 PSK, which
communicates three bits per symbol, 16-quadrature amplitude
modulation (16-QAM), which communicates four bits per symbol,
32-QAM, which communicates five bits per symbol, 64-QAM, which
communicates six bits per symbol, 128-QAM, which communicates seven
bits per symbol, and 256-QAM, which communicates eight bits per
symbol. Modulation assignments with higher communication rates per
subcarrier may also be received.
[0014] An OFDM symbol may be viewed as the combination of the
symbols modulated on the individual subcarriers. Because of the
variable number of bits per symbol modulated on a subcarrier and
the variable number of subchannels that may comprise a wideband
channel, the number of bits per OFDM symbol may vary greatly.
[0015] In accordance with some embodiments, receiver 100 receives
radio frequency (RF) signals through RF and front-end circuitry
102. Circuitry 102 may filter the RF signals received through
antenna 142 with band-pass filter (BPF) 144. Circuitry 102 may also
amplify the RF signals with low-noise amplifier (LNA) 148. RF
signals 103 provided by circuitry 102 may be downconverted to
baseband (e.g., zero-frequency) by in-phase (I) mixer 104 based on
heterodyne frequency 117 generated by heterodyne frequency
generator 116. The baseband signals for the I-channel may be
amplified by baseband amplifier 106.
[0016] Subchannel filter selection switch 108 may couple baseband
signals 107 to a selected one of a plurality of subchannel low-pass
filters 110. Subchannel low pass filters 110 may accumulate signal
information from an associated one of the subchannels during a
filter-input sampling interval. During the filter-input sampling
interval, heterodyne frequency generator 116 provides one of a
plurality of heterodyne frequencies to convert RF signal 103, which
may be received within a selected subchannel, to baseband signal
107. This may allow the downconversion of the proper subchannel
frequency to baseband. The accumulated signal information from each
subchannel may be individually provided by subchannel filters 110
to analog-to-digital converter circuitry 126 for conversion to
digital signals 115.
[0017] For the quadrature-phase (Q) channel component, RF signals
103 may be downconverted to baseband (e.g., zero-frequency) by
mixer 154 based on heterodyne frequency 119 generated by heterodyne
frequency generator 116. Heterodyne frequency 119 may be shifted in
phase by substantially ninety degrees by phase shifter 118. The
baseband signals may be amplified by baseband amplifier 156.
Subchannel filter selection switch 158 may couple the baseband
signals to a selected one of a plurality of subchannel low-pass
filters 160. Subchannel low-pass filters 160 may accumulate signal
information from an associated one of the subchannels during a
filter-input sampling interval. The accumulated signal information
from each subchannel may be individually provided by subchannel
filters 160 to analog-to-digital converter circuitry 166 for
conversion to digital signals 165.
[0018] Digital signal processor (DSP) 120 may, among other things,
perform fast Fourier transforms (FFTs) for each subchannel on
digital signals 115 and 165 (i.e., both the I and the Q channel
components). In some embodiments, FFT circuitry of DSP 120 may
generate a parallel group of time-domain samples for each
symbol-modulated subcarrier that may comprise each of the
subchannels. In some embodiments, DSP 120 may include a plurality
of FFT processing elements.
[0019] In some embodiments, DSP 120 may include an FFT processing
element for each subchannel. In these embodiments, an FFT for each
subchannel may be performed for an OFDM symbol received over a
subchannel.
[0020] In other embodiments in which receiver 100 operates as a
genuine multichannel receiver, FFTs may be performed for OFDM
symbols received over more than one subchannel. In these
embodiments, the FFTs do not need to start their processing
simultaneously.
[0021] In some embodiments, system controller 122 may generate
subchannel selection signal 124 for use by subchannel filter
selection switches 108 and 158 and for use by heterodyne frequency
generator 116. In these embodiments, the selected subchannel
low-pass filter may be associated with a selected subchannel.
Heterodyne frequency generator 116 may be responsive to subchannel
selection signal 124 to generate one of a plurality of heterodyne
frequencies to downconvert RF signals 103 within a corresponding
one of the subchannels during a filter-input sampling interval.
Subchannel filter selection switch 108 may also be responsive to
subchannel selection signal 124 to switch among subchannel low-pass
filters 110, allowing each subchannel filter to accumulate signal
information received from an associated subchannel during the
filter-input sampling interval. In some embodiments, the subchannel
low-pass filters may work in parallel separately accumulating
signal information from each subchannel. In some embodiments,
subchannel filter selection switches 108 and 158 may provide signal
energy to the selected subchannel low-pass filter during a
filter-input sampling interval, allowing the selected subchannel
filter to accumulate signal information and update its state.
[0022] In some embodiments, the filter-input sampling interval may
be occur for each subchannel at least as often as the inverse of a
bandwidth of the subchannel, although the scope of the present
invention is not limited in this respect. The filter-input sampling
interval may be selected to help assure that signal information
from the subchannels is not lost during the sampling of the other
subchannels. In some embodiments that have approximately 20-MHz
subchannels, a filter-input sampling interval may occur at least
once every 50 ns allowing signal information to be accumulated for
each subchannel once every 50 ns, although the scope of the present
invention is not limited in this respect.
[0023] In some embodiments, receiver 100 may be a wideband channel
receiver for receiving OFDM signals in a wideband channel
comprising one or more of the frequency-separated subchannels. In
these embodiments, each subchannel low-pass filter may be
associated with one of the subchannels. In some embodiments, the
subchannel low-pass filters may have a filter bandwidth of
approximately half the subchannel bandwidth. For example, when the
subchannels have a subchannel bandwidth of approximately 20-MHz,
the subchannel low-pass filters have a 3 dB filter bandwidth of
approximately 10-MHz, although the scope of the invention is not
limited in this respect.
[0024] In some embodiments, each of subchannel low-pass filters 110
and each of subchannel low-pass filters 160 may be substantially
identical. For example, in some embodiments, all subchannel
low-pass filters may have the same cutoff frequency and
discrimination order, and they may be of the same filter type.
Examples of suitable filter types include elliptical filters,
Tchebyshev filters, and Butterworth filters, although the scope of
the invention is not limited in this respect.
[0025] In some embodiments, analog-to-digital converter circuitry
126 may comprise whole-channel analog-to-digital converter 114 and
subchannel filter output selection switch 112 (i.e., for the
in-phase channel components). In these embodiments,
analog-to-digital converter circuitry 166 may comprise
whole-channel analog-to-digital converter 164 and subchannel filter
output selection switch 162 (i.e., for the quadrature-phase channel
components). Subchannel filter output selection switch 112 may be
responsive to subchannel filter output selection signal 125 and may
provide an accumulated signal output from a selected one of
subchannel low-pass filters 110 to whole-channel analog-to-digital
converter 114. Subchannel filter output selection switch 162 may
also be responsive to subchannel filter-output selection signal 125
and may provide an accumulated signal output from a selected one of
subchannel low-pass filters 160 to whole-channel analog-to-digital
converter 164. In some embodiments when the wideband channel
comprises up to four or more subchannels, whole-channel
analog-to-digital converters 114 and 164 may comprise at least
9-bit analog-to-digital converters having a sampling rate of at
least as great as a bandwidth of the wideband channel. In the case
of an up to 80-MHz wideband channel, whole-channel
analog-to-digital converters 114 and 164 may have sampling rates of
at least 80-MSPS, although the scope of the invention is not
limited in this respect.
[0026] Whole-channel analog-to-digital converters 114 and 164 may
generate a combination (i.e., not the sum) of signals sampled from
the subchannels. For example, in the case of four subchannels,
every fourth (time-domain) sample provided by whole-channel
analog-to-digital converters 114 and 164 may be associated with the
same subchannel. As an example, whole-channel analog-to-digital
converters 114 and 164 may be suitable for providing samples from
four 20-MHz subchannels, two 40-MHz subchannels, one 80-MHz
wideband channel, although the scope of the invention is not
limited in this respect.
[0027] Subchannel filter output selection signal 125 may cause
switch 112 to switch between outputs of subchannel low-pass filters
110 and may cause switch 162 to switch between outputs of
subchannel low-pass filters 160 allowing subchannel low pass
filters 110 and 160 to be sampled at least once every filter-output
sampling interval. The filter-output sampling interval is explained
in more detail below.
[0028] Although whole-channel analog-to-digital converters 114 and
164 are illustrated as having an 11-bit resolution, this is not a
requirement and whole-channel analog-to-digital converters 114 and
164 with lower or greater resolutions may also be suitable.
Embodiments which receive a greater number of subchannels may
utilize whole-channel analog-to-digital converters 114 and 164 with
greater resolutions and/or sampling rates. In other embodiments,
discussed in more detail below, a single-channel ADC may be used
for each subchannel with lower sampling rates and/or lower
resolutions, which may help reduce cost, among other things.
[0029] In some embodiments, receiver 100 may determine which
subchannels of a wideband channel are being used to convey an OFDM
symbol. In these embodiments, signal detectors may be utilized at
the output of subchannel low-pass filters 110, 160 to detect which
of the subchannels are simultaneously conveying information.
Further signal processing, including analog-to-digital conversion,
may be refrained from being performed on inactive subchannels.
[0030] In some embodiments, RF and front-end circuitry 102 may
comprise attenuator 146 in the RF signal path responsive to
subchannel selection signal 124 to attenuate the RF signal. The
attenuation level may be selected on a per-subchannel basis to
provide a normalized signal level for the analog-to-digital
conversion in circuitry 126 and 166. The use of a normalized signal
level across the subchannels may allow the use of lower resolution
analog-to-digital converters.
[0031] In some embodiments, heterodyne frequency generator 116
comprises fixed-frequency voltage-controlled oscillator (VCO) 132
to generate a constant reference frequency, and a direct digital
synthesizer (DDS) 134 to generate a selected one of a plurality of
stepped frequencies in response to subchannel selection signal 124.
Heterodyne frequency generator 116 may also comprise frequency
combiner 136 to combine the reference frequency and the selected
one of the stepped frequencies to generate heterodyne frequency 117
to downconvert RF signals within the selected subchannel to
baseband signals. In some embodiments, heterodyne frequency
generator 116 may further comprise phase-locked loop (PLL)
synthesizer 140 and frequency divider 138 to operate with VCO 132
to generate heterodyne frequency 117. Other configurations for
selectively generating heterodyne frequencies may also be suitable
for use with embodiments of the present invention. In some
embodiments in which subchannels are separated in frequency by
approximately 20-MHz, the stepped frequencies generated by DDS 134
may be in 20-MHz steps, although the scope of the invention is not
limited in this respect.
[0032] In some embodiments, the frequency spectrums for a wideband
channel may comprise subchannels in either a 5 GHz frequency
spectrum or a 2.4 GHz frequency spectrum. In these embodiments, the
5 GHz frequency spectrum may include frequencies ranging from
approximately 4.9 to 5.9 GHz, and the 2.4 GHz spectrum may include
frequencies ranging from approximately 2.3 to 2.5 GHz, although the
scope of the invention is not limited in this respect, as other
frequency spectrums are also equally suitable.
[0033] In some embodiments, receiver 100 may be part of a personal
digital assistant (PDA), a laptop or portable computer with
wireless communication capability, a web tablet, a wireless
telephone, a wireless headset, a pager, an instant messaging
device, an MP3 player, a digital camera, an access point or other
device that may receive and/or transmit information wirelessly. In
some embodiments, receiver 100 may receive RF communications in
accordance with specific communication standards, such as the EEEE
802.11 (a), 802.11 (b), 802.11 (g/h) and/or 802.16 standards for
wireless local area networks, although receiver 100 may also be
suitable to receive communications in accordance with other
techniques including the Digital Video Broadcasting Terrestrial
(DVB-T) broadcasting standard, and the High performance radio Local
Area Network (HiperLAN) standard. Antenna 142 may comprise one or
more directional or omnidirectional antennas, including, for
example, dipole antennas, monopole antennas, loop antennas,
microstrip antennas or other type of antenna or combination thereof
suitable for reception of RF signals within a frequency spectrum to
be received by receiver 100.
[0034] Although embodiments of the present invention are described
as being suitable for reception and processing of OFDM signals, the
scope of the present invention is not limited in this respect.
Other embodiments may be suitable for receiving and processing
signals having other types of modulation formats.
[0035] Although receiver 100 is illustrated as having several
separate functional elements, one or more of the functional
elements may be combined and may be implemented by combinations of
software-configured elements, such as processing elements including
digital signal processors (DSPs), and/or other hardware elements.
For example, processing elements may comprise one or more
microprocessors, DSPs, application specific integrated circuits
(ASICs), and combinations of various hardware and logic circuitry
for performing at least the functions described herein.
[0036] FIGS. 2A and 2B illustrate subchannel analog-to-digital
converter circuitry in accordance with some embodiments of the
present invention. In these embodiments, analog-to-digital
converter circuitry 226 may be suitable for use as
analog-to-digital converter circuitry 126 (FIG. 1), and
analog-to-digital converters 266 may be suitable for use as
analog-to-digital converter circuitry 166 (FIG. 1). In these
embodiments, analog-to-digital converter circuitry 226 may comprise
a plurality of individual subchannel analog-to-digital converters
214 for the I-phase channel components, and analog-to-digital
converter circuitry 266 may comprise a plurality of individual
subchannel analog-to-digital converters 264 for the Q-phase channel
components. Each subchannel analog-to-digital converter 214 may
receive an accumulated signal output from a corresponding one of
subchannel low-pass filters 110 (FIG. 1), and each subchannel
analog-to-digital converter 264 may receive an accumulated signal
output from a corresponding one of subchannel low-pass filters 160
(FIG. 1).
[0037] In some embodiments, individual subchannel analog-to-digital
converters 214 and 264 may comprise at least 9-bit
analog-to-digital converters having sampling rates of at least as
great as a bandwidth of a subchannel. In some embodiments in which
the subchannels have bandwidths of approximately 20-MHz, the
sampling rate may be at least 20 MSPS. Although individual
subchannel analog-to-digital converters 214 and 264 are illustrated
as 11-bit individual subchannel analog-to-digital converters, this
is not a requirement and embodiments of the present invention may
be implemented with individual subchannel analog-to-digital
converters having lower or greater resolutions.
[0038] The resolutions of individual subchannel analog-to-digital
converters 214 and 264 may be estimated from the modulation order
and the number of subcarriers of a subchannel. In the case of
64-QAM modulation, for each of the subcarriers, at least three bits
of resolution for each I and Q component may be required. When a
subchannel includes forty-eight data subcarriers, six additional
bits of resolution may be required (e.g., the ceiling of base 2 log
of 48). Accordingly, in this example, approximately nine bits of
resolution may be provided by each of individual subchannel
analog-to-digital converters 214 and 264. Additional resolution may
be added for improved noise handling, and a soft decision
capability may also be added for decoding. In general, a
conventional "single" channel receiver, which may process a
wideband channel as a single channel, may require an additional
2-bit (four times) resolution to achieve similar accuracy. This may
be significantly more expensive.
[0039] In some embodiments, an attenuation level provided by an
attenuator, such as attenuator 146 (FIG. 1), may be selected on a
per-subchannel basis to provide a normalized signal level for the
selected subchannel filter and a corresponding one of the
subchannel analog-to-digital converters 214 and 264. The normalized
subchannel signal levels may allow the use of lower resolution
analog-to-digital converters.
[0040] The use of individual subchannel analog-to-digital
converters, instead of a single analog-to-digital converter, such
as whole-channel analog-to-digital converters 114 (FIG. 1) and 164
(FIG. 1), may allow the use of analog-to-digital converters with
lower sampling rates and/or lower resolutions. This may help
significantly reduce manufacturing costs.
[0041] FIG. 3 illustrates a heterodyne frequency generator in
accordance with some embodiments of the present invention.
Heterodyne frequency generator 316 may be suitable for use as
heterodyne frequency generator 116 (FIG. 1), although other
heterodyne frequency generators may also be suitable. Heterodyne
frequency generator 316 comprises a plurality of individual
heterodyne frequency generators 302, each of which may include
fixed-frequency voltage-controlled oscillator (VCO) 332. Each
fixed-frequency voltage-controlled oscillator 332 may generate a
single heterodyne frequency for downconverting a particular
subchannel. Heterodyne frequency generator 316 may also comprise
subchannel heterodyne switch 304 to select a heterodyne frequency
from one of individual heterodyne frequency generators 302 in
response to subchannel selection signal 324. In some embodiments,
subchannel selection signal 324 may correspond to subchannel
selection signal 124 (FIG. 1).
[0042] In some embodiments, each of individual heterodyne frequency
generators 302 may comprise phase-locked loop synthesizer 340 and
frequency divider 338 to operate with voltage-controlled oscillator
332 to generate the heterodyne frequency. Other configurations for
selectively generating heterodyne frequencies are also suitable for
use with embodiments of the present invention.
[0043] FIGS. 4A and 4B illustrate subchannel analog-to-digital
converter circuitry with corresponding amplifiers in accordance
with some embodiments of the present invention. In these
embodiments, analog-to-digital converter circuitry 426 may be
suitable for use as analog-to-digital converter circuitry 126 (FIG.
1), and analog-to-digital converter circuitry 466 may be suitable
for use as analog-to-digital converter circuitry 166 (FIG. 1). In
these embodiments, analog-to-digital converter circuitry 426 may
comprise a plurality of individual subchannel analog-to-digital
converters 414 and associated amplifiers 412 for the I-phase
channel components, and analog-to-digital converter circuitry 466
may comprise a plurality of individual subchannel analog-to-digital
converters 464 and associated amplifiers 462 for the Q-phase
channel components. Each subchannel analog-to-digital converter 414
may receive an amplified accumulated signal output from a
corresponding one of subchannel low-pass filters 110 (FIG. 1), and
each subchannel analog-to-digital converter 464 may receive an
amplified accumulated signal output from a corresponding one of
subchannel low-pass filters 160 (FIG. 1).
[0044] In accordance with some embodiments, amplifiers 412 and 462
may amplify the accumulated signal outputs based on gain control
signals 402 for each subchannel. In these embodiments, an
attenuator in the RF signal path, such as attenuator 146 (FIG. 1),
is not necessarily required because the gain of amplifiers 412 and
462 may be set to provide a normalized signal level to the
analog-to-digital converters.
[0045] In some embodiments, the individual subchannel
analog-to-digital converters 414 and 464 may comprise at least
9-bit analog-to-digital converters having sampling rates of at
least as great as a bandwidth of a subchannel. In some embodiments
in which the subchannels have bandwidths of approximately 20-MHz,
the sampling rate of the analog-to-digital converters may be at
least approximately 20 MSPS. The use of gain control signals 402 to
normalize the output may allow the use of lower resolution
analog-to-digital converters. Although individual subchannel
analog-to-digital converters 414 and 464 are illustrated as having
a resolution of 11-bits, this is not a requirement. Individual
subchannel analog-to-digital converters 414 and 464 with greater
and lesser resolutions may also be suitable.
[0046] FIG. 5 illustrates RF and front-end circuitry in accordance
with some embodiments of the present invention. RF and front-end
circuitry 502 may be suitable for use as RF and front-end circuitry
102 (FIG. 1), although other circuitry may also be suitable. In
these embodiments, a receiver, such as receiver 100 (FIG. 1), may
utilize more than one of spatially-diverse antennas 542 to "divide"
a single subchannel into one or more spatial channels. In some
embodiments, each antenna 542 may receive signals from one spatial
channel. In some embodiments, each spatial channel may be used to
communicate separate or independent data streams on the same
subcarriers as the other spatial channels, allowing the reception
of additional data without an increase in frequency bandwidth. In
other embodiments, each spatial channel may be used to communicate
the same data as the other spatial channels. In these embodiments,
the use of spatial channels may take advantage of the multipath
characteristics of a particular subchannel. In some embodiments,
the spatial channels may be non-orthogonal channels (e.g., may
overlap in frequency and or time) and in some embodiments, each
spatial channel may use the same subcarriers as the other spatial
channels.
[0047] In some embodiments, an OFDM symbol may be received over a
single subchannel comprising a plurality of spatial channels. Each
spatial channel may comprise the same set of orthogonal
subcarriers. In some embodiments, a single subchannel may have a
bandwidth of approximately 20-MHz, although the scope of the
invention is not limited in this respect.
[0048] In some embodiments, RF circuitry 502 may comprise antenna
selection switch 540 to select one of antennas 542 in response to
spatial channel selection signal 524. In these embodiments, which
may be referred to as open-loop multiple-input, multiple-output
(MIMO) embodiments, each of antennas 542 may correspond to one of
the spatial channels. In some embodiments, circuitry 502 may filter
the RF signals received through antennas 542 with an associated one
of band-pass filters (BPFs) 544, although the scope of the
invention is not limited in this respect. In some embodiments, each
of subchannel low-pass filters 110 (FIG. 1) may be associated with
one of the spatial channels, and each of subchannel low-pass
filters 160 (FIG. 1) may also be associated with one of the spatial
channels. In these embodiments, the individual subchannel low-pass
filters may accumulate signal information from a particular spatial
channel during a filter-input sampling interval. Spatial channel
selection signal 524 may correspond to subchannel selection signal
124 (FIG. 1) and may cause antenna selection switch 540 to select
an antenna for receiving each spatial channel during the
filter-input sampling interval.
[0049] In some embodiments, which may be referred to as closed-loop
MIMO embodiments, the spatial channels may be orthogonal spatial
channels, and a one-to-one correspondence between antennas 542 and
spatial channels is not required. In these embodiments, the
orthogonal spatial channels may be generated with beamforming
techniques at the transmitter, and received using beamforming
techniques at the receiver. In these embodiments, DSP 120 (FIG. 1)
may be configured to perform receiving beamforming to extract the
information from the orthogonal spatial channels, which can be
referred to as orthogonalization of spatial channels. The use of
orthogonal spatial channels may help reduce crosstalk between
spatial channels in comparison with open-loop embodiments.
[0050] In some embodiments, a heterodyne frequency generator may
provide a single heterodyne frequency to convert RF signals of the
single frequency subchannel to baseband signals. The spatial
channel low-pass filters may accumulate signal information for a
corresponding one of the spatial channels during the appropriate
filter-input sampling interval.
[0051] FIGS. 6A, 6B and 6C illustrate timing diagrams in accordance
with some embodiments of the present invention. FIG. 6A
qualitatively depicts two consecutive 50 ns sampling intervals.
Each 50 ns time interval may be a filter-input sampling interval
and may include a sampling subinterval for each subchannel. First
filter-input sampling interval 602 may be at the end of a current
OFDM symbol, and filter-input sampling interval 604 may be at the
beginning of a next OFDM symbol. In this example, receiver 100
(FIG. 1) may receive four signals 606, 608, 610 and 612 from four
subchannels simultaneously. Signal 614 illustrates the sum of
signals 606, 608, 610 and 612, which may be viewed as the overall
signal coming on a wideband channel (which is 80-MHz in this
example).
[0052] Signal 606 during filter-input sampling subinterval 616
(i.e., from 0 ns to 12.5 ns) may be downconverted to baseband using
a controlled heterodyne frequency. During sampling subinterval 616,
both I and Q subchannel filter selection switches 108 and 158 may
connect their outputs respectively to a first subchannel low-pass
filter (for both the I and Q channel components, respectively) and
the baseband signals from the first subchannel are filtered.
[0053] In next filter-input sampling subinterval 618 (i.e., from
12.5 ns to 25 ns), signal 608 may be downconverted to baseband
using a controlled heterodyne, and both I and Q subchannel filter
selection switches 108 and 158 may connect their outputs to a
second subchannel low-pass filter (for both the I and Q channel
components, respectively), and the baseband signals from the second
subchannel are filtered.
[0054] In the next filter-input sampling subinterval 620 (i.e.,
from 25 ns to 37.5 ns), signal 610 may be downconverted to baseband
using a controlled heterodyne, and both I and Q subchannel filter
selection switches 108 and 158 may connect their outputs to a third
subchannel low-pass filter (for both the I and Q channel
components, respectively), and the baseband signals from the third
subchannel are filtered.
[0055] In the next filter-input sampling subinterval 622 (i.e.,
from 37.5 ns to 50 ns), signal 612 may be downconverted to baseband
using a controlled heterodyne, and both I and Q subchannel filter
selection switches 108 and 158 may connect their outputs to a
fourth subchannel low-pass filter (for both the I and Q channel
components, respectively), and the baseband signals from the fourth
subchannel are filtered.
[0056] This process may be performed for each subchannel and is not
limited to the example of four subchannels. This process may also
be repeated at least as often as the inverse of the bandwidth of a
subchannel, although the scope of the invention is not limited in
this respect.
[0057] Wideband signal processing with a synchronous switching of
heterodyne frequency and subchannel low-pass filters may result in
the subchannel low-pass filter output signal level to be just about
the same as if it were obtained using a separate subchannel
receiver for each subchannel normalized for the associated
subchannel. In some cases when there are four subchannels, the
subchannel low-pass filter output level may be about four-times
less than the output level of a low-pass filter in an equivalent
single subchannel receiver, because about one-fourth of the signal
energy is accumulated by the subchannel low-pass filters. Little or
no signal-to-noise ratio (SNR) degradation may occur, because the
noise power may also be reduced by a factor of about four, keeping
the SNR about the same as for a single subchannel receiver. In some
embodiments of the present invention, power loss may be compensated
by providing additional gain before subchannel low-pass filters 110
(FIG. 1) and 160 (FIG. 1). Circuitry 426 (FIG. 4A) and circuitry
466 (FIG. 4B) illustrate examples of this, although the scope of
the invention is not limited in this respect.
[0058] Although filter-input sampling intervals 602 and 604 are 50
ns intervals illustrated as having four sampling subintervals of
12.5 ns, this is not a requirement as it illustrates embodiments
having four 20-MHz bandwidth subchannels comprising a wideband
channel of having an 80-MHz bandwidth. Accordingly, the scope of
the present invention is not limited in this respect. In some
embodiments, the length of intervals 602 and 604 depend on the
subchannel bandwidth, and the number of sampling subintervals may
depend on the number of subchannels in a wideband channel.
[0059] FIG. 6B illustrates attenuator signal output in accordance
with some embodiments of the present invention. Signal levels
received on different subchannels may have different average power
levels, which may result in different signal levels at the output
of the subchannel low-pass filters. Higher resolution
analog-to-digital converters are generally required to digitize
such signals. Higher resolution analog-to-digital converters tend
to be very expensive. In some embodiments, a per-subchannel
automatic gain control may be implemented with an attenuator, such
as attenuator 146 (FIG. 1). As illustrated in FIG. 6B, attenuator
output signal 624 during subinterval 616 may provide an attenuation
level to normalize the input signal to a first subchannel low-pass
filter to within the dynamic range of a subsequent
analog-to-digital converter. During subinterval 618, the attenuator
output signal may be changed based on the signal level from the
next subchannel. This process may be performed during a
filter-input sampling interval for each subchannel and may provide
a more normalized output for analog-to-digital conversion, allowing
the use of lower resolution analog-to-digital converter
circuitry.
[0060] In alternate embodiments, instead of a selectable attenuator
in the RF signal path, baseband amplifiers with automatic gain
control may be provided before the subchannel low-pass filters. An
example of this is illustrated in FIGS. 4A and 4B.
[0061] FIG. 6C illustrates baseband signal inputs to subchannel
low-pass filters in accordance with embodiments of the present
invention. Baseband signal inputs 626, 628, 630 and 632 may
correspond respectively to subchannel signals 606, 608, 610 and 612
received respectively during sampling subintervals 616, 618, 620
and 622. As illustrated, baseband signal inputs 626, 628, 630 and
632 may be normalized to within the range of a subsequent
analog-to-digital converter. Subchannel signals 606, 608, 610 and
612 are also illustrated as being sampled respectively during
sampling subintervals 634, 636, 638 and 640 of next interval 604 at
the beginning of the next OFDM symbol. In some embodiments, the
sampling for a subchannel may be repeated at least as often as the
inverse of a bandwidth of a subchannel, although the scope of the
present invention is not limited in this respect. The filter-input
sampling interval may be selected to help assure that signal
information from the subchannels is not lost during the sampling of
the other subchannels. In the examples illustrated in FIGS. 6A, 6B
and 6C with 20-MHz subchannels, a sampling interval may occur for
each subchannel at least once every 50 ns, although the scope of
the invention is not limited in this respect.
[0062] FIG. 7 is a flow chart of a signal reception procedure in
accordance with some embodiments of the present invention.
Procedure 700 may be performed by a receiver, such as receiver 100
(FIG. 1) to receive an OFDM symbol over one or more subchannels
comprising a wideband channel.
[0063] In operation 702, RF circuitry of a receiver may
simultaneously receive RF signals over one or more subchannels.
Operation 702 may be performed by RF circuitry 102 (FIG. 1),
although the scope of the invention is not limited in this
respect.
[0064] In operation 704, a heterodyne frequency may be generated to
downconvert the RF signals in the first subchannel to baseband. The
proper heterodyne frequency may be generated for the first
subchannel in response to a subchannel selection signal which may
select the first subchannel. In some embodiments, baseband signals
for an I-channel and Q-channel may be generated. Operation 704 may
be performed by heterodyne frequency generator 116 (FIG. 1),
although the scope of the invention is not limited in this
respect.
[0065] In operation 706, the baseband signals may be provided to a
subchannel low-pass filter associated with the first subchannel. A
subchannel filter selection switch may be responsive to the
subchannel filter input selection signal to provide the baseband
signal to the proper subchannel low-pass filter. Operation 706 may
be performed by subchannel filter selection switches 108 and 158
(FIG. 1), although the scope of the invention is not limited in
this respect.
[0066] In operation 708, the selected subchannel low-pass filter
may accumulate signal information from the baseband signal during a
portion of a filter-input sampling interval. During the
filter-input sampling interval time, the selected subchannel
low-pass filter may update its state. Operation 708 may be
performed during a portion of the filter-input sampling interval
which may be repeated at least as often as the inverse of the
subchannel bandwidth. Operation 708 may be performed by one of
subchannel low-pass filter 110 (FIG. 1) for the I-channel
component, and one of subchannel low-pass filters 160 (FIG. 1) for
the Q-channel component, although the scope of the invention is not
limited in this respect.
[0067] Operation 710 performs an analog-to-digital conversion on
the accumulated signal output of the first subchannel low-pass
filter. Operation 710 may be performed by analog-to-digital
conversion circuitry 126 (FIG. 1) for the I-channel component, and
analog-to-digital conversion circuitry 166 (FIG. 1) for the
Q-channel component, although the scope of the invention is not
limited in this respect. In some embodiments, operation 710 may
perform an analog-to-digital conversion on the accumulated signal
output of the first subchannel low-pass filter during a
filter-output sampling interval.
[0068] Operation 712 generates the subchannel filter input
selection signal to switch to a next subchannel, and operations 704
through 708 may be repeated for the next subchannel. The subchannel
selection signal may be generated by a system controller, such as
system controller 122 (FIG. 1), although the scope of the invention
is not limited in this respect. Operations 704 through 708 may be
performed for each subchannel during the subchannel input sampling
interval. Operation 710, on the other hand, may be performed for
each subchannel for each filter-output sampling interval. The
filter-input sampling interval and the subchannel output sampling
interval may be at least as great as the inverse of subchannel
bandwidth. In the case of 20-MHz subchannels, these sampling
intervals may occur less than about every 50 ns, allowing
operations 704 through 710 to be performed for each subchannel, at
least once every 50 ns. Although subchannel input sampling interval
and the subchannel output sampling interval may be equal, nothing
requires this. Subchannel output sampling interval may be based on
a multiple of the subchannel bandwidth to allow FFT processing.
Subchannel input sampling interval may be selected to, among other
things, decrease unwanted impulse disturbances from the RF portion
of receiver 100 (FIG. 1) to the ADCs and the DSP.
[0069] Once enough samples are received, operation 714 performs an
FFT on the digital signals generated from the subchannels (and for
both the I and Q channel components) to demodulate an OFDM symbol
for subsequent use in generating a decoded bit stream. Operation
714 may be performed by DSP 120 (FIG. 1), although the scope of the
invention is not limited in this respect.
[0070] In some embodiments, procedure 700 may further comprise
selecting an attenuation level in response to the subchannel
selection signal to provide a normalized baseband signal level at
the inputs of the subchannel low-pass filters. In other
embodiments, procedure 700 may further comprise providing a gain
control signal to baseband amplifiers to normalize the baseband
signal level inputs of the subchannel low-pass filters.
[0071] In some other embodiments, procedure 700 may be performed by
a receiver to receive an OFDM symbol over a single subchannel
comprising a plurality of spatial channels. In these embodiments,
each of a plurality of spatially diverse antennas may receive
signals from one spatial channel. In some embodiments, each spatial
channel may be used to communicate separate or independent data
streams on the same subcarriers as the other spatial channels,
allowing the reception of additional data without an increase in
frequency bandwidth. In other embodiments, each spatial channel may
be used to communicate the same data as the other spatial
channels.
[0072] Although the individual operations of procedure 700 are
illustrated and described as separate operations, one or more of
the individual operations may be performed concurrently, and
nothing requires that the operations be performed in the order
illustrated.
[0073] Embodiments of the invention may be implemented in one or a
combination of hardware, firmware and software. Embodiments of the
invention may also be implemented as instructions stored on a
machine-readable medium, which may be read and executed by at least
one processor to perform the operations described herein. A
machine-readable medium may include any mechanism for storing or
transmitting information in a form readable by a machine (e.g., a
computer). For example, a machine-readable medium may include
read-only memory (ROM), random-access memory (RAM), magnetic disk
storage media, optical storage media, flash-memory devices,
electrical, optical, acoustical or other form of propagated signals
(e.g., carrier waves, infrared signals, digital signals, etc.), and
others.
[0074] The Abstract is provided to comply with 37 C.F.R. Section
1.72 (b) requiring an abstract that will allow the reader to
ascertain the nature and gist of the technical disclosure. It is
submitted with the understanding that it will not be used to limit
or interpret the scope or meaning of the claims.
[0075] In the foregoing detailed description, various features are
occasionally grouped together in a single embodiment for the
purpose of streamlining the disclosure. This method of disclosure
is not to be interpreted as reflecting an intention that the
claimed embodiments of the subject matter require more features
than are expressly recited in each claim. Rather, as the following
claims reflect, invention lies in less than all features of a
single disclosed embodiment. Thus the following claims are hereby
incorporated into the detailed description, with each claim
standing on its own as a separate preferred embodiment.
* * * * *